Engine, engine exhaust temperature controlling apparatus, and controlling method

ABSTRACT

The present invention has been realized in order to keep the cylinder exhaust temperature of a gas engine within a predetermined range, and thereby prevent the generation of misfire and knocking. In the present invention, in S 1,  when the number of rotations of the engine is greater than a predetermined number, in S 2,  the exhaust temperatures of the cylinders are sampled at predetermined intervals, in S 3,  an average of the exhaust temperatures is calculated, in S 4,  the load factor at that point is determined, in S 5,  the average exhaust temperature T ave  is compared with the exhaust temperature T( n ) of each cylinder, and it is determined whether the deviation ΔT n  is greater or smaller than the set deviation T limit  for that load factor. When the deviation ΔT n  is smaller, the exhaust temperature is within the set deviation and there is no need to adjust the fuel spray period, and therefore the sequence returns to S 2.  When the deviation ΔT n  is greater, in S 6,  it is determined whether to increase or reduce the opening period of the electronic fuel spray valve. When increasing the opening period, the sequence shifts to S 7,  and when reducing the opening period, the sequence shifts to S 8.  Then, in S 9,  if the engine exceeds the predetermined number of rotations, the processes of S 2  to S 6  are repeated; in S 9,  if the engine is below the predetermined number of rotations, the control operation ceases.

BACKGROUND OF INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to an invention for controlling anelectronic fuel spray valve in an engine such as a gas engine, therebyautomatically adjusting the exhaust temperatures of cylinders so as toreduce variation between them, and more specifically relates to anengine which can be controlled in this way, and a controlling apparatusand a method for controlling the engine exhaust temperature, which makesuch control possible.

[0003] 2. Description of Related Art

[0004] In a multi-cylinder engine, the temperatures of the exhausts fromthe cylinders do not match, and, in engines for commercial use,variation in the exhaust temperatures of the cylinders is presentlyregulated to less than an average of ±15° C. at a load of 100%. Theexhaust temperature of a cylinder which has exceeded this range isadjusted by manually adjusting a gas-adjusting valve of the cylinder,thereby balancing the exhaust temperatures of the cylinders.

[0005] However, since the gas-adjusting valve is adjusted at a load of100%, there is greater variation between the exhaust temperatures of thecylinders at loads other than 100%. Furthermore, even at a load of 100%,the set value of the gas-adjusting valve deviates from its initialsetting as years pass, so that the set value may require readjustment.Unless this deviation in the set value due to the passage of time isdealt with, variation in the exhaust temperatures of the cylinders willgreatly increase, causing misfire and knocking.

[0006] Such misfire and knocking leads to considerable disadvantageswhen, for example, operating a co-generation system. That is, in aco-generation system, when the engine suffers misfire or knocking, theengine output (the amount of electricity generated by the system) isreduced as a first step of human or mechanical safety procedures, and,as a second step, the engine is stopped; the result of reducing theengine output and stopping operating is not only to cease supplying theexpected power, but may sometimes be non-profitable, after compensationclaims of power contract infringement (demand-over).

[0007] Therefore, a technique for automatically controlling the exhausttemperatures in the cylinders, so as to reliably balance the exhausttemperatures in the cylinders while the engine is operational, isdesirable. This technique is also important in, for example, safely andstably operating the co-generation system mentioned above.

[0008] This invention has been realized in view of the problemsdescribed above, and aims to provide an exhaust temperature controltechnique which can automatically control variation in the exhausttemperatures of the cylinders, and prevent misfire and knocking bykeeping the exhaust temperatures of the cylinders within a predeterminedrange.

DISCLOSURE OF INVENTION

[0009] A first aspect of this invention provides an engine comprising aplurality of cylinders, and a plurality of electronic fuel spray valveswhich supply fuel and are provided in correspondence with thesecylinders: the engine having an exhaust temperature measuring unit whichmeasures the exhaust temperatures of said cylinders, and outputs exhausttemperature signals for each of said cylinders; and a control unit whichsamples the exhaust temperature signals from the exhaust temperaturemeasuring unit at predetermined time intervals, calculates an averageexhaust temperature of all the plurality of cylinders, and, in the casewhere deviation, determined by comparing this average exhausttemperature with the exhaust temperatures of the cylinders, exceeds apredetermined set deviation, controls the opening period of theelectronic fuel spray valve of the corresponding cylinder by apredetermined amount of control.

[0010] A second aspect of this invention provides an exhaust temperaturecontrol apparatus of an engine for supplying fuel via an electronic fuelspray valve to a plurality of cylinders comprising: an exhausttemperature measuring unit which measures the exhaust temperatures ofsaid cylinders, and outputs exhaust temperature signals for each of saidcylinders; and a control unit which samples the exhaust temperaturesignals from the exhaust temperature measuring unit at predeterminedtime intervals, calculates an average exhaust temperature of all theplurality of cylinders, and, in the case where deviation, determined bycomparing this average exhaust temperature with the exhaust temperaturesof the cylinders, exceeds a predetermined set deviation, controls theopening period of the electronic fuel spray valve of the correspondingcylinder by a predetermined amount of control.

[0011] A third aspect of this invention provides an exhaust temperaturecontrol apparatus of an engine which comprising a plurality of cylinderswhich fuel is supplied to via electronic fuel spray valves, comprising:an exhaust temperature measuring unit which measures the exhausttemperatures of said cylinders, and outputs exhaust temperature signalsfor each of said cylinders; a load factor measuring unit which detectsthe load factor of said engine and outputs a load signal; and a controlunit which sets a set deviation and control amount in accordance withthe load factor of said engine, determines the present load factor ofsaid engine based on the load signal from said load factor measuringunit, samples the exhaust temperature signals from the exhausttemperature measuring unit at predetermined time intervals, calculatesan average exhaust temperature of all the plurality of cylinders, and,in the case where deviation, determined by comparing this averageexhaust temperature with the exhaust temperatures of the cylinders,exceeds the set deviation in the present load factor, controls theopening period of the electronic fuel spray valve of the correspondingcylinder by a control amount corresponding to the present load factor.

[0012] A fourth aspect of this invention provides an exhaust temperaturecontrol method of an engine having a plurality of cylinders in whichfuel is supplied to from a plurality of electronic fuel spray valves,comprising the steps of: measuring the exhaust temperatures of saidcylinders at predetermined time intervals, outputting exhausttemperature signals for each of said cylinders; calculating an averageexhaust temperature of all the plurality of cylinders, and, in the casewhere deviation, determined by comparing this average exhausttemperature with the exhaust temperatures of the cylinders, exceeds apredetermined set deviation, controlling the opening period of theelectronic fuel spray valve of the corresponding cylinder by apredetermined amount of control.

[0013] A fifth aspect of this invention provides an engine comprising: aplurality of cylinders, a plurality of electronic fuel spray valveswhich are provided in correspondence with these cylinders and openingperiod thereof can be controlled by control signals, exhaust temperaturemeasuring units which are provided in correspondence with said pluralityof cylinders and output the exhaust temperatures of said cylinders asexhaust temperature signals, and a load factor measuring unit whichdetects the load factor of the engine and outputs a load signal; whereina computer which controls said engine being used as a control unit,which sets a set deviation and control amount in accordance with theload factor of said engine, determines the present load factor of saidengine based on the load signal from said load factor measuring unit,samples the exhaust temperature signals from the exhaust temperaturemeasuring unit at predetermined time intervals, calculates an averageexhaust temperature of all the plurality of cylinders, and, in the casewhere deviation, determined by comparing this average exhausttemperature with the exhaust temperatures of the cylinders, exceeds theset deviation in the present load factor, controls the opening period ofthe electronic fuel spray valve of the corresponding cylinder by acontrol amount corresponding to the present load factor.

BRIEF DESCRIPTION OF DRAWINGS

[0014]FIG. 1 is a schematic view of an embodiment of this invention.

[0015]FIG. 2 is a control image diagram illustrating the essentialpoints in controlling the exhaust temperature in the embodiment of thisinvention.

[0016]FIG. 3 is an image diagram showing the relationship between loadfactor and setting deviation in the embodiment of this invention.

[0017]FIG. 4 is an image diagram showing the relationship between loadfactor and duration rate in the embodiment of this invention.

[0018]FIG. 5 is a flowchart showing a sequence of controlling theexhaust temperature of an engine in the embodiment of this invention.

[0019]FIG. 6 is a manipulation image diagram of a case where the openingperiod of an electronic fuel control valve is increased in theembodiment of this invention.

[0020]FIG. 7 is a manipulation image diagram of a case where the openingperiod of an electronic fuel control valve is decreased in theembodiment of this invention.

[0021]FIG. 8 is a diagram showing an embodiment of changeover time inthe exhaust temperature of an engine which has been controlled by thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] A preferred embodiment of this invention will be explained withreference to FIGS. 1 to 6.

[0023]FIG. 1 is a schematic view of an embodiment of this invention. Agas engine of this invention has a plurality of cylinders. An electronicfuel spray valve 1 is attached to the cylinder head 2 of each cylinder.Each electronic fuel spray valve 1 is connected via a fuel gas pipe 3 toan unillustrated fuel supply source, and supplies gas fuel to acombustion chamber inside the cylinder. Further, an exhaust temperaturegauge unit 4 is attached to each of the cylinder heads 2 of thecylinders. The exhaust temperature gauge units 4 measure the exhausttemperature near the exit of the each cylinder, and output an exhausttemperature signal 10 to a control unit 5, which is explained later. Forexample, a temperature gauge such as a pyrometer can be used as theexhaust temperature gauge unit 4. Incidentally, FIG. 1 shows onecylinder, and therefore show one electronic fuel spray valve 1 and oneexhaust temperature gauge unit 4, however in fact, the electronic fuelspray valve 1 and the exhaust temperature gauge unit 4 are attached toeach of a plurality of cylinders.

[0024] Furthermore, the gas engine of this invention comprises anexhaust temperature control unit 5 (hereinafter abbreviated as “controlunit”) which controls an opening period of the electronic fuel sprayvalve 1 in order to keep the exhaust temperature of the cylinders withina predetermined range. The exhaust temperature gauge unit 4 and theelectronic fuel spray valve 1 of each cylinder are connected to thecontrol unit 5, and the exhaust temperature signal 10 is input from theexhaust temperature gauge unit 4; in addition, a control signal 11 isoutput to each electronic fuel spray valve 1, the opening period of eachof the electronic fuel spray valves 1 being adjusted so as to keep theexhaust temperature within the predetermined range.

[0025] More specifically, a computer, which adjusts the opening periodof the electronic fuel spray valves 1 by processing data according to apredetermined sequence described later, and a governor, which has beenset so that the same controls as the computer are executed, are used asthe control unit 5.

[0026] Moreover, the gas engine of this embodiment comprises a loadfactor measuring unit 6 which measures the load factor of the engine,and a rotation number measuring unit 7 which measures the number ofrotations of the engine. These are connected to the control unit 5, andrespectively output a load factor signal 12 and a rotation number signal13 to the control unit 5. The signals 12 and 13 are used as data by thecontrol unit 5 to adjust the opening period of the electronic fuel sprayvalves 1.

[0027] The gas engine of this embodiment is used as an engine forco-generation, and drives an unillustrated electric generator.Therefore, the load of the engine described above corresponds to thegenerated electrical power, and the load factor signifies the powerrate. More specifically, a signal representing the power generated bythe electric generator is sent to an unillustrated generator board, andthe signal is output as the load factor signal 12 from the generatorboard to the control unit 5. That is, in the case of this embodiment,the electric generator and the generator board function as the loadfactor measuring unit 6.

[0028] Furthermore, a non-contact type rotation number detecting elementusing light, provided in the rotation drive section of the engine, canbe used as the rotation number measuring unit 7.

[0029] An input unit 8 for setting predetermined data required forcontrol is connected to the control unit 5 of the gas engine of thisembodiment. The predetermined data required for control comprises thefollowing (1) to (5).

[0030] (1) Control Start (End) Number of Rotations [rpm]

[0031] This is the number of rotations of the engine when the controlstarts when the number of rotations exceeds this value, and ends whenthe number of rotations falls below this value.

[0032] (2) Sampling Set Time [sec]

[0033] This is the time interval for sampling the exhaust temperaturesignal, and can be set within a range of 0.1 seconds to 60 seconds inthis embodiment.

[0034] (3) Set Load [%]

[0035] This is the one or more load value which is set as the controlsplit point in controlling this embodiment, eight values of L0 to L7being set in this embodiment.

[0036] (4) Duration Rate R_(dur) [deg·Crank Angle/sec]

[0037] This signifies the changing speed of the amount of control whichis set in accordance with the values of the set load. The amount ofcontrol represents the opening period (in units of [degCA] ) of theelectronic fuel spray valve 1, which is directly controlled by thecontrol unit 5 in this embodiment. In this case, a changing amount ofthe opening period of the valve per a second is shown by the crankangle. For example, 0.1 degCA represents the open angle of the fuelspray valve is increased or decreased with 0.1 degCA in a second.

[0038] (5) Set deviation T_(limit) [° C.]

[0039] This is the value which determines the permissible range of thedeviation between the actual exhaust temperature of each cylinder at thetime of sampling, and the average exhaust temperature of all thecylinders of the gas engine. This value is set independently from theduration rate at each set load.

[0040]FIG. 2 schematically shows the control of the exhaust temperaturein the engine of this embodiment. The control sequence and function ofthe control unit 5 in this embodiment will be explained with referenceto this figure.

[0041] The control unit 5 regularly samples the exhaust temperature ofeach cylinder and the load of the engine at predetermined time intervals(t_(samp) [seconds]), and determines the set deviation (T_(limit) [°C.]) in accordance with the load; in addition, in the control of thisembodiment, the control unit 5 calculates the average exhausttemperature (T_(ave) [° C.]) of all the cylinders.

[0042] The deviation upper limit value and deviation lower limit valuein FIG. 2 respectively represent (average exhaust temperatureT_(ave)+set deviation T_(limit)) [° C.] and (average exhaust temperatureT_(ave)—set deviation T_(limit)) [° C.]. Even in the case where one ofsix cylinders departs from the range of the set deviation at a giventime, as shown by the broken line in FIG. 2, according to the exhausttemperature control of this embodiment, the exhaust temperature of thecylinder is adjusted to within the range of the set deviation (betweenthe deviation upper limit and deviation lower limit).

[0043] Here, in the control shown in FIG. 2, at a sampling set time of,for example, 0.1 seconds, the control unit 5 performs the abovecalculation every 0.1 seconds. Furthermore, at a sampling set time ofsixty seconds, the control unit 5 performs the above calculation everysixty seconds. In this embodiment, the sampling set time is two seconds.

[0044] In the above calculation, at each sampling set time, the controlunit 5 measures the exhaust temperature at the cylinder exit of eachcylinder, calculates the average exhaust temperature of all thecylinders, compares the average exhaust temperature with the actualexhaust temperatures at the cylinder exits of the cylinders, anddetermines whether the exhaust temperature of each cylinder is below thepredetermined set deviation. As mentioned above, this set deviation isthe plus-minus (upper limit and lower limit) deviation with respect tothe average value of the exhaust temperature. Then, the control unit 5controls the electronic fuel spray valve 1 of any cylinder where thedifference between the average exhaust temperature and the actualexhaust temperature departs from the set deviation.

[0045] At the time of controlling the electronic fuel spray valve 1, theopening amount of the electronic fuel spray valve 1 is changed by usingthe duration rate, and the exhaust temperature of the cylinder beingcontrolled is adjusted so as to be within the set deviation.Incidentally, as described above, the set deviation and the durationrate can be set to different values at each set load.

[0046]FIG. 3 shows the relationship between the set load (load factor,horizontal axis) and the duration rate R_(dur) [deg·Crank Angle/sec](vertical axis). Any number of set loads from L₀ to L_(n) can be set; inthis embodiment, n=7 and there are a total of eight set loads. Forinstance, L₀ is set at 0%, L₁ at 25%, etc. Furthermore, as shown in FIG.3, the duration rate between the points of the set loads (L₀, L₁, . . .) is set so as to link them in straight lines.

[0047]FIG. 4 shows the relationship between the set load (load factor,horizontal axis) and the set deviation T_(limit) (vertical axis).Similarly in the case of set deviation, any number of set loads from L₀to L_(n) can be set; in this embodiment, n=7 and there are a total ofeight set loads, as described above. Incidentally, the set loads at thistime can be set independently from the set loads of the duration rate.Further, as shown in FIG. 4, each point of the set loads (L₀, L₁, . . .) is set so as to link them in straight lines.

[0048] Furthermore, when the set deviation is set at 10° C., forexample, the permissible range for the average exhaust temperature ofthe cylinders becomes plus or minus 10° C., and no control is carriedout as long as the difference between the actual exhaust temperature andthe average exhaust temperature is within this range; control is carriedout when the difference is departed from this range.

[0049]FIG. 5 is a flowchart showing a sequence for controlling theexhaust temperature according to a control program which is written inthe control unit 5. In FIG. 5, reference numerals S1 to S9 correspond tosteps 1 to 9. The control sequence whereby the control unit 5 and theprogram written therein act in co-operation, and the control functionsof the control unit 5 which are thereby realized, will be explained withreference to FIG. 5.

[0050] As shown in FIG. 5, after the engine is started, when the controlunit 5 starts to operate, in step S1, the control unit 5 detects thenumber of rotations of the engine based on the rotation number signal13, output by the rotation number measuring unit. Here, when the numberof rotations of the engine is, for example, more than 950 rpm, a controloperation is carried out and the sequence proceeds to step S2. On theother hand, when the number of rotations or the engine is below 950 rpm,no control operation is carried out, and step 1 is repeated after anappropriate interval. Incidentally, the number of rotations of theengine at which control should be carried out can be set as desired fromthe input unit.

[0051] In step 2, the control unit 5 starts sampling the exhausttemperature. That is, based on the exhaust temperature signal 10 whichwas output from the exhaust temperature gauge unit 4, the control unit 5detects the exhaust temperature of each cylinder at each predeterminedsampling set time t_(samp) [seconds].

[0052] In step 3, the control unit 5 instantly calculates the averageexhaust temperature T_(ave) [° C.] from the exhaust temperatures of thecylinders, input at each sampling set time t_(samp) [seconds].

[0053] In step 4, the control unit 5 determines the load factor of theengine from the load factor signal 12, output by the load factormeasuring unit 6. Then, from this load factor, the control unit 5calculates the set deviation T_(limit) [° C.] to determine whether tocontrol the electronic fuel spray valve 1 based on FIG. 4, and inaddition, when it has been determined to control the electronic fuelspray valve 1 based on FIG. 3, the control unit 5 calculates theduration rate R_(dur) [deg·CA/sec] to be used. Moreover, the controlunit 5 compares the average exhaust temperature T_(ave) [° C.], whichwas calculated in step 3, with each (maximum of eighteen cylinder,minimum of sixteen cylinders) exhaust temperature T(_(n)) [° C.], andcalculates the deviation ΔT_(n) [° C.] between them.

[0054] In step 5, the control unit 5 determines whether the absolutevalue |ΔT_(n)| of the deviation ΔT_(n) [° C.] in the cylinders isgreater or smaller than the set deviation T_(limit) [° C.] in theabovementioned load factor, and thereby determines whether to controlthe electronic fuel spray valve 1 of each cylinder.

[0055] In the case where |ΔT_(n)|>T_(limit), control is necessary sincethe exhaust temperature deviation ΔT_(n)[° C.] of the cylinder exceedsthe set deviation T_(limit) [° C.]. Therefore, the sequence proceeds tothe subsequent step 6 (equation (1) in step 5 of FIG. 5). In the casewhere ΔT_(n)≦T_(limit), there is no need to adjust the fuel spray periodin the electronic fuel spray valve 1 of the cylinder, since the exhausttemperature deviation ΔT_(n) [° C.] of the cylinder is within the setdeviation T_(limit) [° C.]. Therefore, the control unit 5 returns tostep 2 and repeats the same sequence (equation (2) in step 5 of FIG. 5).

[0056] In step 6, the control unit 5 calculates the code of the exhausttemperature deviation ΔT_(n)[° C.], and determines whether the presentexhaust temperature T(_(n)) [° C.] of the cylinder has departed towardthe high temperature side or the low temperature side. That is, whenΔT_(n)>0 (equation (1) in step 6 of FIG. 5), the exhaust temperatureT(_(n))<the average exhaust temperature T_(ave), and it is determinedthat the present exhaust temperature T(_(n)) [° C.] of the cylinder hasdeparted toward the low temperature side. When ΔT_(n)<0 (equation (2) instep 6 of FIG. 5), the exhaust temperature T(_(n))>the average exhausttemperature T_(ave), and it is determined that the present exhausttemperature T(_(n)) [° C.] of the cylinder has departed toward the hightemperature side.

[0057] In step 6, when the exhaust temperature T(_(n)) of thecylinder<the average exhaust temperature T_(ave) (i.e. when ΔT_(n)>0),the present exhaust temperature of the cylinder has departed from thelower limit value toward the low temperature side, and consequently, thecontrol unit 5 proceeds to step 7, where the exhaust temperature of thecylinder is increased. That is, the control unit 5 uses the durationrate R_(dur)[deg·CA/sec], which is the changing speed of the openingperiod of the electronic fuel spray valve 1 of the cylinder and isdetermined in step 4, to calculate a target value for the opening periodas shown in FIG. 6, applies the output signal 11 to the electronic fuelspray valve 1, and changes the opening period of the electronic fuelspray valve 1. More specifically, when tc represents the time lapse fromdetermining that control was required in step 5 and passing the loop ofsteps 9, 2, 3, 4, . . . until it is finally determined in step 5 thatcontrol is unnecessary and control is stopped, the target value for theinitial value Do of the target value of the opening period of the valveis expressed by the following equation.

[0058] Target value of opening period [degCA]=D₀+D_(c)

[0059] Here, D_(c)[degCA]=R_(dur)[degCA/sec]×tc[sec].

[0060] Furthermore, in step 6, when the exhaust temperature T(_(n)) ofthe cylinder>the average exhaust temperature T_(ave) (i.e. whenΔT_(n)<0), the present exhaust temperature of the cylinder has departedfrom the higher limit value toward the high temperature side, andconsequently, the control unit 5 proceeds to step 8, where the exhausttemperature of the cylinder is decreased. That is, the control unit 5uses the duration rate R_(dur)[deg·CA/sec], which is the changing speedof the opening period of the electronic fuel spray valve 1 of thecylinder and is determined in step 4, to calculate a target value forthe opening period as shown in FIG. 7, applies the output signal 11 tothe electronic fuel spray valve 1, and changes the opening period of theelectronic fuel spray valve 1. More specifically, when tc represents thetime lapse from determining that control was required in step 5 andpassing the loop of steps 9, 2, 3, 4, . . . until it is finallydetermined in step 5 that control is unnecessary and control is stopped,the target value for the initial value Do of the target value of theopening period of the valve is expressed by the following equation.

[0061] Target value of opening period [degCA]=D₀D1c

[0062] Here, D, [_(deg)CA]’_(R) _(dur), [degCA/sec]×tc [sec].

[0063] After the fuel spray amount has been adjusted by adjusting theopening period of the electronic fuel spray valve 1 to keep it withinthe set deviation during the duration control, (i.e. in step 7 and step8), in step 9, the control unit 5 detects the number of rotations of theengine in the same manner as in step 1 and, when the number of rotationsof the engine is greater than, for example, 950 rpm, the controlsequence returns to step 2 and repeats the procedures of steps 2 through7, and 8. As a consequence, by increasing or decreasing the openingperiod of the electronic fuel spray valve 1 with the duration rateR_(dur) [degCA/sec], set at each load of the engine, cylinders whichhave departed from their set deviations are continuously controlled sothat their exhaust temperatures are kept within the set deviation. Whenthe number of rotations of the engine is less than 950 rpm in step 9,the control operation stops. Incidentally, the same reference number ofrotations is set in step 1 and step 9.

[0064] In the control described above, variation in the exhausttemperature is generally greater when at low load, and smaller at highload. When variation in the exhaust temperature at low load is reducedin the same way as at high load, there is a possibility that unwarrantedcontrol will diffuse the exhaust temperature (make it non-divergent).Conversely, it is sometimes difficult to carry out control when theduration rate value is high at high load, and the control speed may bereduced when the duration rate value is low at low load. That is, theduration rate has appropriate amount of adjustment which variesaccording to the load.

[0065] To deal with this, the set deviation and duration rate at eachload may be changed so that the exhaust temperature remains within anexhaust temperature range which is appropriate for that load. Generally,the set deviation and duration rate tend to increase as the loaddecreases, and decrease and medium and high load. Since the setdeviation and duration rate are independent, there is a merit thatprecise control appropriate for the load can be performed.

[0066]FIG. 8 is a graph showing effects of controlling the engineaccording to this embodiment.

[0067] In this case, the operational status of the engine is changedfrom a load factor of 50% to one of 80%, and the load factor is thenreturned to 50%. The set deviation T_(limit)[° C.] is set to plus orminus 10° C. from the exhaust temperature average value at the cylinderexits of all the cylinders. The duration rate R_(dur) [degCA/sec] is setto 0.05 [degCA/sec] at a load factor of between 50% and 80%.

[0068] In FIG. 8, there is a cylinder having an exhaust temperaturewhich has departed from the deviation upper limit and deviation lowerlimit of the set deviation at the point where the load factor isapproximately 65%. Usually, unless controlled, the exhaust temperaturewould not be restored and the cylinders would operate with unbalancedexhaust temperatures; however, due to the effect of the control, asshown in FIG. 8, the exhaust temperature is thereafter restored towithin its normal range. Thus, according to the control, even incircumstances where there is a possibility of variation in the exhausttemperatures, the variation can be automatically corrected, and as aresult, knocking and misfire caused by an unbalance in the exhausttemperatures of the cylinders can be prevented.

[0069] Incidentally, the engine used in the embodiment described abovehas a cylinder diameter of 220 mm and six cylinders, but the presentinvention can achieve similar effects even when the cylinder diameterand number of cylinders are changed. Furthermore, although the durationrate and the set deviation are divided into a total of eight loads, thisnumber can be increased or decreased as necessary.

[0070] Furthermore, although this embodiment relates to a gas engine, itcan be applied in any other type of gas engine in which the openingperiod of an electronic fuel spray valve is adjusted in order to controlthe exhaust temperature.

1. An engine comprising: a plurality of cylinders, and a plurality ofelectronic fuel spray valves which supply fuel and are provided incorrespondence with these cylinders; wherein the engine having anexhaust temperature measuring unit which measures the exhausttemperatures of said cylinders, and outputs exhaust temperature signalsfor each of said cylinders; and a control unit which samples the exhausttemperature signals from the exhaust temperature measuring unit atpredetermined time intervals, calculates an average exhaust temperatureof all the plurality of cylinders, and, in the case where deviation,determined by comparing this average exhaust temperature with theexhaust temperatures of the cylinders, exceeds a predetermined setdeviation, controls the opening period of the electronic fuel sprayvalve of the corresponding cylinder by a predetermined amount ofcontrol.
 2. An exhaust temperature control apparatus of an engine forsupplying fuel via an electronic fuel spray valve to a plurality ofcylinders, comprising: an exhaust temperature measuring unit whichmeasures the exhaust temperatures of said cylinders, and outputs exhausttemperature signals for each of said cylinders; and a control unit whichsamples the exhaust temperature signals from the exhaust temperaturemeasuring unit at predetermined time intervals, calculates an averageexhaust temperature of all the plurality of cylinders, and, in the casewhere deviation, determined by comparing this average exhausttemperature with the exhaust temperatures of the cylinders, exceeds apredetermined set deviation, controls the opening period of theelectronic fuel spray valve of the corresponding cylinder by apredetermined amount of control.
 3. An exhaust temperature controlapparatus of an engine comprising a plurality of cylinders which fuel issupplied to via electronic fuel spray valves, comprising: an exhausttemperature measuring unit which measures the exhaust temperatures ofsaid cylinders, and outputs exhaust temperature signals for each of saidcylinders; a load factor measuring unit which detects the load factor ofsaid engine and outputs a load signal; and a control unit which sets aset deviation and control amount in accordance with the load factor ofsaid engine, determines the present load factor of said engine based onthe load signal from said load factor measuring unit, samples theexhaust temperature signals from the exhaust temperature measuring unitat predetermined time intervals, calculates an average exhausttemperature of all the plurality of cylinders, and, in the case wheredeviation, determined by comparing this average exhaust temperature withthe exhaust temperatures of the cylinders, exceeds the set deviation inthe present load factor, controls the opening period of the electronicfuel spray valve of the corresponding cylinder by a control amountcorresponding to the present load factor.
 4. An exhaust temperaturecontrol method of an engine having a plurality of cylinders in whichfuel is supplied to from a plurality of electronic fuel spray valves,comprising the steps of: measuring the exhaust temperatures of saidcylinders at predetermined time intervals and outputting exhausttemperature signals for each of said cylinders; calculating an averageexhaust temperature of all the plurality of cylinders, and; in the casewhere deviation, determined by comparing this average exhausttemperature with the exhaust temperatures of the cylinders, exceeds apredetermined set deviation, controlling the opening period of theelectronic fuel spray valve of the corresponding cylinder by apredetermined amount of control.
 5. An engine comprising: a plurality ofcylinders, a plurality of electronic fuel spray valves which areprovided in correspondence with these cylinders and opening periodthereof can be controlled by control signals, exhaust temperaturemeasuring units which are provided in correspondence with said pluralityof cylinders and output the exhaust temperatures of said cylinders asexhaust temperature signals, and a load factor measuring unit whichdetects the load factor of the engine and outputs a load signal; whereina computer which controls said engine being used as a control unit,which sets a set deviation and control amount in accordance with theload factor of said engine, determines the present load factor of saidengine based on the load signal from said load factor measuring unit,samples the exhaust temperature signals from the exhaust temperaturemeasuring unit at predetermined time intervals, calculates an averageexhaust temperature of all the plurality of cylinders, and, in the casewhere deviation, determined by comparing this average exhausttemperature with the exhaust temperatures of the cylinders, exceeds theset deviation in the present load factor, controls the opening period ofthe electronic fuel spray valve of the corresponding cylinder by acontrol amount corresponding to the present load factor.